Residential area made possible through large-scale in-situ polluted soil remediation

The former factory site of bus manufacturer Den Oudsten Bussen B.V. in Woerden was to become a new residential area. However, this would not be possible without carrying out large-scale soil remediation first. More than 30,000 cubic meters of soil up to 60 meters depth was contaminated with oil, aromatics and solvents like chlorinated hydrocarbons (CHCs). We started on this in-situ soil remediation project, one of the largest ever in the Netherlands, in 2018. It will take a total of five to seven years to decontaminate all the soil. 

In-situ bioremediation

We are tackling this soil remediation process in steps. First of all, we excavated and removed around 5,000 cubic meters of soil down to the groundwater level. This was then cleaned by a qualified soil remediation specialist. We remediated the contaminated groundwater in-situ, on location. The total amount of contaminated soil concerned is approximately one million cubic meters containing more than 15,000 kilograms of contamination. We clean the soil using bioremediation, specifically “bioaugmentation”.  

With this method we stimulate the biological breakdown of the contaminants by adding a special carbon source and nutrients to the soil. We also add bacterial cultures that dechlorinate the contaminants. The nutrients encourage the bacteria in the soil to flourish and devour the contaminants, so to speak. While carrying out this soil remediation, the transformation of the site into a residential area has already begun. This makes our project even more critical. We therefore continuously coordinate our activities with other works like laying pipes and cables, road construction, home building, and landscaping.

Bioremediation without (chemical) waste

By applying bioaugmentation we encourage the soil to break down the contaminants on its own, without a water treatment plant and with no chemical waste. The bacteria doing all this work come from a laboratory. We pump up the groundwater downstream, add the nutrients and bacteria, and then inject it into the soil upstream so that it spreads through the area again. This cycle is repeated in seven phases, over a period of two to three years.It takes time before the conditions for biodegradation are optimal. It will then take a few years before the contaminants are broken down completely. 

Our task was clear: break down at least 95% of the contaminants. To enable this we set up a complex infrastructure for our environmental services. We installed 44 extraction filters at depths of 25, 40 and 60 meters. These filters are connected to the remediation unit through more than five kilometers of pipeline. We make water treatment units and other equipment for soil remediation ourselves. Our trade secret is the perfect mixture of bacteria and nutrients. One thing isclear, this type of remediation is truly specialist work. Bioremediation is the technology for the future: this soil decontamination method is much more sustainable and often faster and cheaper.